docs(types): Update PHPDoc comments for type hints in Client class

- Updated type hints in PHPDoc comments for messages and responses in the Client class to use more specific types
- Changed `iterable<Message>` to `iterable<array-key, Message>`
- Changed `list<Response|ResponseInterface>` to `array<array-key, Response|ResponseInterface>`

Author: guanguans

README.md

@@ -131,8 +131,8 @@ $response = $promise->wait();
 ### Concurrent requests
 
 ```php
-/** @var list<\Guanguans\Notify\Foundation\Contracts\Message> $messages */
-/** @var list<\Guanguans\Notify\Foundation\Response|\Psr\Http\Message\ResponseInterface> $responses */
+/** @var iterable<array-key, \Guanguans\Notify\Foundation\Contracts\Message> $messages */
+/** @var array<array-key, \Guanguans\Notify\Foundation\Response|\Psr\Http\Message\ResponseInterface> $responses */
 $responses = $client->pool($messages);
 ```
 

src/Foundation/Client.php

@@ -75,12 +75,12 @@ public function sendAsync(Message $message): PromiseInterface
     }
 
     /**
-     * @param iterable<Message> $messages
+     * @param iterable<array-key, Message> $messages
      *
      * @throws \GuzzleHttp\Exception\GuzzleException
      * @throws \Throwable
      *
-     * @return list<Response|ResponseInterface>
+     * @return array<array-key, Response|ResponseInterface>
      */
     public function pool(iterable $messages): array
     {